Adjustable pitch propeller



Sept. 28, 1%? A. E. GABA ADJUSTABLE PITCH PROPELLER Filed May '15, 1936INVENTOR ACH ILLE ERNEST GABA ATTO R N EY5 Patented Sept. 28, 1931UNITED STATES PATENT OFFICE 10 Claims.

vision of improved apparatus for connecting the blade of an adjustablepitch propeller to a r0- tatable propeller hub. The present applicationis a continuation in part of my copending application Serial No.757,536, filed December 14, 1934, which issued on September 22, 1936, asUnited States Patent No. 2,054,810.

In my above-mentioned copending application, an adjustable pitchpropeller is described in which propeller blades are received withincylindrical stub branches extending outwardly from a rotatable propellerhub and are secured to the hub by means of a core comprising a pair ofinterconnected helically threaded cylinders and a stud. The threads ofone of the cylinders of the core engages corresponding threads providedin the foot of the propeller blade and the threads of the other cylinderof the core engages threads provided upon a, cylindrical member disposedwithin the stub branch and extending outwardly from the hub. The studengages a second set of threads formed in a recess in the propellerblade and is secured to the core.

In the structure described above, the centrifugal force tending to tearthe blades from the hub when the assembly is rotating is resisted whollyby the threaded cylindrical member whose threads engage the threadsof'the core. The

present invention provides improved apparatus for connecting the bladesto the rotatable hub in such a manner that a centripetal force isapplied to the propeller blades to offset in part the centrifugal forceof the rotating blades and thereby to provide an improved distributionof the forces acting while the propeller assembly is rotating.

In the apparatus of the invention, a substantiallycylindricalblade-support member having an outwardly. extending flangeadjacent its lower end is rigidly associated with a propeller bladeadjacent the foot of the blade, and appropriate means are provided forexerting a force upon the flange of the blade-support member to aid inholoding the blade in operative relation with the The structure of theinventionincludes a main connecting element for connecting the blade tothe hub which comprises a threaded stud engaging the propeller bladeadjacent the foot thereof and also engaging a threaded inner coresecured toand extending outwardly from the hub. The blade-support memberis rigidly connected to the stud and to the blade. An outer cylindricalcore extending outwardly from the hub and surrounding the blade-supportmember is provided with an annular cap extending substantially radiallyinwardly. The relation of the annular cap with respect to the flange ofthe blade 5 support member is such that the cap'is positionedsubstantially directly over the flange. A ball or roller bearing isseated against the flange, and spring means seated against the undersideof the cap exert a force on the ball or roller bear- 1o ing assembly andthrough it to the flange of the blade-support member, thereby applying acentripetal force to the blade when the propeller assembly is rotatingto aid in holding the propeller blade in operative relation with respectto 15 the hub.

A substantially cylindrical housing member associated with the capsurrounds the foot of the blade. A bushing member associated with theupper end portion of the housing member is 20 adapted to provide abearing surface against the foot of the blade. A relatively hard ringmember associated with the blade advantageously is provided to furnish abearing surface upon which the bushing acts.

The invention will be better understood from the following descriptionconsidered in conjunction with the accompanying drawing, in which Fig. lis an elevation, partially in section, showing the relation of theapparatus of the inven- 30 tion to an adjustable pitch propellerassembly;

Fig. 2 is a longitudinal cross section through a structure according tothe invention by which a. propeller blade is connected to a rotatableFig. 3 is a transverse cross section taken substantially along the line3-3 of Fig. 2; and

Fig. 4 is a cross section through a modified spring assembly.

.A propeller hub I0 is mounted by means 014.40 a plate II and a capscrew II! on a propeller shaft l3. Mechanism I4 for adjusting the pitchof propeller blades is housed within the annular space between the huband the propeller shaft and in a casing l5, and the entire assembly isnected to the crank shaft of a motor I 6. An outwardly extendingcylindric'al'inner core I! is secured to the hub (preferably it isformed integrally therewith) and is provided with helical threads l8formed on its inner surface. A 50 propeller blade 20, the foot of whichis suitably recessed, is positioned adjacent the cylindrical inner coreH. A stud 2| provides means for connecting the propeller blade to thehub through the cylindrical con- 45' core I1, and this stud-constitutesthe main connecting element between the propeller blade and the hub. Thestud 2| is threaded adjacent its upper end portion to engage threads 22formed in the propeller blade 20 and adjacent its lower end to engagethe helical threads l8 of the core IT. The assembly is such that if aturning moment is applied to the stud 2|, the propeller blade will beturned about its longitudinal axis toadjust the pitch of the blade. I

A substantially cylindrical blade-support member 23 is rigidly securedto the blade. The conthe ring member 42 are advantageously formed ofvery hard steel and are accurately machined to reduce to a minimum thefrictional resistance 7 to turning the blade about its longitudinalaxis.

ne'ction between the blade-support member and the blade is effectedprincipally through the intermediary of the stud. The upper portion ofthe blade-support member 23 extends radially inwardly and is providedwith threads 24 engaging a section of the helical threads formed on thestud 2| adjacent the point at which the stud enters into engagement withthe propeller blade. The blade support member thus in effect becomes alock-nut on the stud to hold it rigidly in engagement with the blade,the blade, stud,and bladesupport member becoming thereby a solidarystructure. A pin 25 extending through the blade, the blade-supportmember, and the stud locks these three elements in position.

The lower portion of the blade-support member 23 is provided with anannular flange 26 extending radially outwardly beyond the periphery 'ofthe foot of the blade 20. A ball or roller bearing- 2I is seated againstthe flange 2., which advantageously constitutes the lower face thereof.An annular ring 28 forms the upper faceaet the bearing.

An outer cylindrical core 30 extending outwardly from the hub Illsurrounds the flange 26 of the blade support member and extends to apoint substantially above the flange. Suitable stops 3| engaging theouter cylindrical core 36 and the upper face 28 of ball or rollerbearing hold the latter in non-rotatable relation with respect to theouter core 30.

An annular cap 32 extending radially inwardly is secured to the outercylindrical core 30 by a threaded clamping ring 33 engaging threadssuitably formed on the outer cylindrical core. The

annular cap 32 is positioned substantially directly over the flange-26of the blade-support member.

A series of compression springs 34, seated against the undersurface ofthe annular cap'32, 1

arelmounted within the space between the cylindrical core 30 and theouter surface of the blade 20 to exert a force upon the upper faceof-the ball' or roller bearing and through it upon the flange 26 of theblade-support member to aid in holding the blade in operative relationwith respect to the hub. The springs 34 are guided by shafts 35 mountedon the upper face 28 ofthe ball or roller bearing'and extending upwardlyinto suitably formed recesses 36 in the annular cap 32. The recesses 36are suificiently deep to allow slight movement of the guide shafts 35into and out of them.

In place of the compression springs 34 describe above, other means forapplying force to the flange 26 of the blade-support member 23 may beadopted. For example, as shown in Fig. 4, a series of dished washers 31mounted one over the other on the guide shafts 35 to act in the mannerof springs may be employed if desired.

A substantially cylindrical housing member 40 extends upwardly from theannular cap 32 and surrounds the foot of theblade 20. A bushing Acylindrical hoop 42' provided with a flange 43 surrounding. the bladefoot aids in retaining the ring member 42 in position and in preventinglateral distortion of the blade foot.

An oil-seal 44 is provided adjacent the bushing 4| to lubricate it andto' keep dirt and grit from gaining access to the mechanism. Theoil-seal is closed by a ring 45 in threaded engagement with the upperend portion of the cylindrical housing member 4| The apparatus oftheinvention is such that an improved distribution of the forces exertedat the foot of the blade when the propeller assembly is in operation isattained. A considerable portion of the centrifugal-force tending tothrow the blade from the hub is taken by. the stud 2| and the innercylindrical core H, but these members are relieved from taking the fullmagnitude of such forces by virtue of the pressure exerted by thesprings 34 on the flange 26 of the blade-support member. The pressure ofthe springs constitutes a centripetal force acting in opposition to thecentrifugal force of the rotating blade. Suppose the-centrifugalforce ofthe blade has a value F-and the counter-force exerted by the springs 34'on the blade-supporting member 23 has a value f. The resultant pressureon the screw-thread of the inner core I! will be Ff. The arrangement ofthe invention thus provides for a better distribution of the stressesencountered in retaining the blade in position, since the threaded innercore I! participates in these stresses only to the extent of the valueof F-f, the outer cylindrical core 30 participating therein to theextent'of the'value of 1.

Due to the fact that the coefficient of the friction on the ball orroller bearing is much lower than the coefficient of the friction of thescrewthread, the frictional resistance to be overcome in order to causethe blade to turn in adjusting the pitch thereof during flight is madeless. If tan 1/1 equals the coefficient of friction of the screwthreads, and tan 6 the coeflicient of fricition of the bearing roller,then for a centrifugal force F the frictional resistance F0 on the screwthreads is, as pointed out in my above-mentioned copending patent,

(where a is the pitch of the screw threads) whereas with thecompensating device of the invention, exerting a centripetal force f, Iwill have a frictional resistance F0 due to the screw threads amountingonly to Fc'=(Ff) cos a tan 1/ and on the ball bearing a frictionalresistance fc Of fc= (f) tan 6 tion of the propeller assembly comprisingan outwardly extending flange associated with the blade adjacent thelower end thereof and means exerting a downwardly acting force on theflange.

2. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable propeller hub, and means for adjusting the pitch ofthe blade, apparatus for connecting the blade to the hub comprising amain connecting element, and means for relieving the stress imposed onthe main connecting element during operation of the propeller assemblycomprising an outwardly extending flange associated with the bladeadjacent the lower end thereof and spring means exerting a downwardlyacting force on the flange:

3. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable propeller hub, and means for adjusting the pitch ofthe blade, apparatus for connecting the blade to the hub comprising astud secured in the lower end portion of the blade, means connecting thestud to the hub, an outwardly extending flange associated with the bladeadjacent the lower end thereof, and means exerting a downwardly actingforce on the flange to relieve the stress imposed on the stud duringoperation 'of the propeller assembly.

4. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable propeller hub, and means for adjusting the pitch ofthe blade, apparatus for connecting the blade to the hub comprising astud secured in the lower end portion of the blade, means connecting thestud to the hub, an outwardly extending flange associated with the bladeadjacent the lower end thereof, and a plurality of springs exerting adownwardly acting force on the flange to relieve the stress imposed onthe stud during operation r of the propeller assembly.

5. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable propeller hub, and means for adjusting the pitch ofthe blade, apparatus for connecting the blade to the hub comprisingastud' secured in the lower end portion of the blade and engaging withthe hub to secure the blade tothe hub and resist the centrifugal forcetending to tear the blade from the hub during rotation of the hub, anoutwardly extending flange associated with the blade adja-' cent thefoot thereof, and means for exerting a centripetal force on the flangeduring rotation of the hub to relieve the stress imposed by thecentrifugal force of the blade on the stud.

6. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable propeller hub, and means for adjusting the pitch ofthe-blade, apparatus for connecting the blade to the hub comprising aninner core extending outwardly from the hub, a stud secured in the lowerendportion of the blade and engaging with to the hub comprising an Ipropeller hub, and

the inner core, an outwardly .extendingflange associated with the bladeadjacent the lower end thereof, an outer core extending outwardly fromthe hub and surrounding the flange, and

means associated with the outer core exerting a downwardly acting forceon the flange.

'7. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable propeller hub, and means for adjusting the pitch ofthe blade, apparatus for connecting the blade inner internally threadedcore extending outwardly from the hub, a stud secured in the lower endportionof the blade and engaging'with the threads of inner core, anoutwardly extending flange associated with the blade adjacent the lowerend thereof,

an outer core extending outwardly from the hub and surrounding theflange, an annular cap secured to the outer core, and means bearingagainst the annular cap and exerting a downwardly acting force on theflange.

8. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable propeller hub, and means for adjusting the pitch ofthe blade, apparatus for connecting the blade to the hub comprising aninner internally threaded core extending outwardly from the hub,

a stud secured in the lower end portion or the blade and engaging withcore, an outwardly extending flange associated with the blade adjacentthe lower end thereof, an outer core extending outwardly from the huband surrounding theflange, an annular cap secured to the outer core, andspring means seated against the annular cap and exerting a downwardlyacting force on the flange.

9. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable means for adjusting the pitch of the blade, apparatusfor connecting the blade to the hub comprising an inner internallythreaded core extending outwardly from the hub, a stud secured in thelower end portion of the blade and engaging with the threads of innercore, an outwardly extending flange associated with the blade adjacentthe lower end thereof,

, an anti-friction bearing seated on the flange, an

outer core extending outwardly from the hub and surrounding the flange,an annular cap secured to the outer core, and a plurality of springsbearing against the annular cap and exerting a downwardly acting forceon the anti-friction bearing.

10. In an adjustable pitch propeller assembly comprising a propellerblade, a rotatable propeller hub, and means for adjusting the pitch ofthe blade, an outer core extending outwardly from the hub andsurrounding the lower end of the blade, an annular cap secured to theouter core, a substantially cylindrical housing member extendingupwardly from the annular cap and surrounding the lower end portion ofblade, and a bushing associated with the upper end of the housing andproviding a bearing surface for the blade.

ACHILLE ERNEST GABA.

the threads of inner

